JAM-2434 Ngix custom recipe

This recipe allows us to modify the ```/etc/nginx/servers/jammer/custom.conf``` nginx config file and, currently, used in order to set ```passenger_spawn_method``` to ```direct```.

In ```/etc/nginx/nginx.conf``` there is a ```include /etc/nginx/servers/*.conf```, this include occurs within the main http block. In ```/etc/nginx/servers/jammer.conf``` there is also ```include /etc/nginx/servers/jammer/custom.conf```. This include occurs within the server block for the application.

P.S.,
The recipe was deployed to staging, so we can also verify if this setting indeed applies.